The Lights work off 12 volt (Battery/Converter) the A/C may use 12 volts for control.. Also the Fridge and water heater and furnace.
Your problem is a lack of 12 volts
Tribble shooting guide
Is The RV 30 or 50 amp. If 50 amp and thigns like the TV and microwave still work make sure the plug is well set and the park breakers are both set (turn off hard and on)
If 50 amp on a 30 amp site you may have a bad adapter
If 30 amp skip the above If Microwave and TV working read on
Check your breakers.. The one marked CONV turn off and on
Finally check your converter (may be part of power distribution panel) post make and model and use a voltmeter on the output.. I'm guessing there is none or very low
If that is the case get a 30 amp SMART CHARGER and hook it to the house batteries till you can fix.
UNLESS
FUSES.. There are fuses as part of the converter, usually 2 or 3, These must be replaced all at the same time by the way (Small converters may have just one)
UNPLUG and wait a few mintues before repalcing if they test bad
HOW TO TEST
using the voltmeter probe the small square openings at each end of the top of a blade fuse.. Should be same voltage.. Or the clips on a cartridge fuse (same should be) Differnet voltages = blown fuse Cartridge fuses = UPGRADE YOUR CONVERTER.
If the converter is part of the power panel the fuses are usually the two on the right and usually 30 amp.